Patent GB-1331117-A (GB)
Title: Bonding of metallic panels
IPC: B23K11/00
Filed: 1970-12-10
Abstract: 1331117 Welding by pressure; making honeycomb panels J R CAMPBELL 10 Dec 1970 58796/70 Headings B3A and B3R A panel for use in aeronautical and astronautical environments, comprises two electrically conductive metal face sheets 12, 14, and an electrically conductive metal honeycomb core 16 comprising corrugated strips 18 having edge flanges 24 by which the strips are intermittently nested with each other and welded to the face sheets. The welding together of the panel is effected in two stages, viz. (1) in which the core strips 18 are successively inserted between and resistance welded to the sheets, this welding being sufficient merely to maintain sheet/core location and the current being low enough to avoid undesirable welding phenomena (e.g. stresses, deformations, oxidation); and (2) in which the thus resistance welded panel is integrated by welding by diffusion, or by inductive current in a reducing atmosphere. Metals for sheets and core may, e.g. be titanium alloy or stainless steel. In a described example, the sheets and core strips are respectively 0À040 and 0À003 inch thick, In forming the corrugated strips, interflange webs 62 thereof are bowed, as shown in Fig. 6, so that where the strips nest adjacent bowed webs engage so that they are welded to each other during the stage (2) welding, whether or not there is a stage (1) welding of these webs. Prior to the stage (1) welding, the sheets and core strips are cleansed as by pickling, or flooding by deionized water, and burrs and chips are removed. In the stage (1) welding, pairs of spaced longitudinally movable electrode rollers 26 co-operate with a supporting electrode bar 30 which carries a core strip 18 and is inserted between spaced sheets 12, 14. The longitudinal spacing of each pair of rollers 26 is preferably such that when one roller overlies a triple metal layer comprised by a sheet and the nesting portions of two core strips flanges, the other roller overlies only a double metal layer comprised by a sheet and a single flange portion, this arrangement balancing current flow. Further, the electrode bar 30 comprises small and large projections 34, 36 (Fig. 4) for engagement respectively with nested and unnested portions of the core strip to provide for greater and lesser current densities respectively. Stage (1) welding is effected with pressures of 20,000- 40,000 p.s.i. In Fig. 3, a single transformer 40 is used with each pair of rollers 26, whereas in a preferred circuit (Fig. 5), providing substantially identical current flow to each of the rollers, each of two firing controls 44 is connected to the primaries 52, 54 of two transformers 46, 48, the secondaries 56, 58 of which are connected to the rollers 26 and the electrode bar 30. The stage (2) welding may be effected by diffusion welding in an automatic vacuum furnace. Titanium getter shields of C.P. titanium may be provided to avoid excessive heat radiation and gas contamination. For stainless steel panels, a dry hydrogen atmosphere may be used. The panels may be suspended or placed upon flat platens during diffusion welding. The Specification discloses example temperatures, heating rates, vacuum levels.